You know, I have a hard time remembering whether it was with my ex boyfriend, or whether it was a random kiss during an anime convention where this girl came up to me and said she shipped our charas, and wanted to kiss me, so I did. The fact that I don't remember between the two kinda tells you how special it was, tbh.
My most memorable one was with a girl that I dated before, actually. I have better memories of that one than I do of my actual first kiss. lol